Method for controlling a ventilator, and system therefor

ABSTRACT

A method for controlling breathing gas flow of a ventilator for assisted or controlled ventilation of a patient as a function of a tracheobronchial airway pressure of the patient. A ventilator tube, such as a tracheal tube or tracheostomy tube, can be introduced into a trachea of the patient and subjected to the breathing gas, and has an inflatable cuff and at least one lumen that is continuous from a distal end of the tube to a proximal end of the tube. An apparatus detects an airway pressure, in which the tracheobronchial airway pressure is ascertained by continuous or intermittent detection and evaluation of an intra-cuff pressure prevailing in the cuff of the tube inserted into the trachea. The breathing gas flow of the ventilator is controlled as a function of the intra-cuff pressure detected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for controlling the breathing gasflow of a ventilator for assisted or controlled ventilation of a patientas a function of the tracheobronchial airway pressure of the patient,having a ventilator tube, such as a tracheal tube or tracheostomy tube,that can be introduced into the trachea or the patient and subjected tothe breathing gas, that has an inflatable cuff and at least one lumenthat is continuous from the distal end of the tube to the proximal endof the tube. This invention also relates to an apparatus for detectingthe airway pressure, in which the tracheobronchial airway pressure isdetermined by continuous or intermittent detection and evaluation of theintra-cuff pressure prevailing in the cuff of the tube inserted into thetrachea, and the breathing gas flow of the ventilator is controlled as afunction of the intra-cuff pressure detected.

This invention also relates to a system for assisted or controlledventilation of a patient, having a ventilator with a breathing gassource and a ventilator tube, which has an inflatable cuff with a supplyline for compressed air, such as a tracheal tube or tracheostomy tube,which can be connected to the breathing gas source, an apparatus fordetecting the airway pressure, and a control device which as a functionof patient values, such as the airway pressure, controls the ventilator,or the supply quantity and composition of the breathing gas to the tube.

This invention also relates to the use of a ventilator tube, such as atracheal tube or tracheostomy tube, or a gastric probe in a system forassisted or controlled ventilation of a patient with a ventilator.

2. Description of Related Art

A ventilator for assisted or controlled ventilation, with a ventilatortube and a breathing gas source that can be made to communicate with theventilator tube and is controllable with patient values, is known fromEuropean Patent Disclosure EP 0 022 144 A1. With the aid of the controldevice of the ventilator, respiratory parameters such as tidal volume,respiratory rate, respiratory minute volume, flow pattern over time,end-inspiratory pause, amplitude of the breathing gas flow, pressure atthe end of inspiration, peak pressure, PEEP pressure, idle volume in theventilator, and ventilator compliance, can be adjusted.

In all the known ventilators and ventilation methods known, theso-called ventilation pressure, that is, the airway pressure (Presp)prevailing in the airways, is output as a parameter or is used as aparameter in the control algorithms of the ventilator. In clinicalpractice, Presp is typically ascertained inside the ventilator, or inthe tubing leading to the patient. The airway pressure measured in theventilator, because of the flow-dependent flow resistance inside theequipment, vent hoses, and ventilator tube, however, often differsconsiderably from the so-called central or tracheobronchial airwaypressure (Ptrach) prevailing in the trachea of the patient. It istherefore difficult to draw a conclusion about the central airwaypressure actually achieved in the trachea from the ventilation pressuremeasured inside the ventilator.

European Patent Disclosure EP 0 459 284 B1 teaches measuring the centralairway pressure via a pressure measuring hose additionally placed in thetrachea or in the tracheal tube, or via a fluid-filled pressuremeasuring conduit machined into the wall of the tracheal tube. Thetracheobronchial airway pressure thus is intended to provide improvedcontrol of ventilators with supporting spontaneous breathing modes. Adisadvantage in this measuring method for detecting the tracheobronchialairway pressure using pressure hoses in accordance with European PatentDisclosure EP 0 459 284 B1 is that the thin pressure measuring hoses,placed in the trachea in the tracheal tube, rapidly plug up withsecretions on their end oriented toward the bronchial tube, and thus thecentral airway pressure can no longer be measured reliably. The pressuremeasuring hoses must be rinsed out from time to time. An apparatusaccording to European Patent Disclosure EP 0 459 284 B1 for measuringthe tracheobronchial airway pressure using pressure measuring hoses orpressure measuring conduits that are filled with fluid has not yetgained acceptance, mainly because of the high cost of equipment and theexpected vulnerability to malfunction, or the resultant measurementimprecision.

German Patent Disclosure DE-A 32 04 110 discloses a tracheal tube thatincludes a ventilation hose and a pressure measuring cannula formeasuring the airway pressure. The pressure measuring hose ends insidethe ventilator tube, at a distance from the distal end of the ventilatortube. This apparatus is again used to detect the airway pressure forregulating ventilation control with a ventilator. This apparatus fordetecting the central airway pressure again has the disadvantage thatthe pressure measuring cannula, which is open on its end toward thebronchial tube, easily becomes plugged with secretions, making reliable,artifact-free measurement and regulation of the ventilator impossible.

PCT International Application WO 94/22518 teaches a ventilator tubewhich is used to control a ventilator. For continuous measurement of thecentral tracheobronchial airway pressure in assisted or controlledventilation, the ventilator tube has a pressure sensor, located near thedistal end of the ventilator tube. The pressure sensor is connected toan electronic signal processor, and the signal obtained is used tocontrol various functions in the ventilator. Such a method istechnologically complex and once again, because of deposits of secretionon the sensor, is adequately invulnerable to malfunction.

SUMMARY OF THE INVENTION

One object of this invention is to provide a method and a system withwhich the tracheobronchial airway pressure prevailing in the trachea ofa patient to be ventilated can be determined and used to control thebreathing gas supply to a ventilator, continuously and largely free ofartifacts, without hindrance from secretions or transitory kinking ofpressure measuring cannulas that are, for example integrated into thetube shaft. Based on known methods for controlling the breathing gasflow in a ventilator, this object is achieved according to thisinvention by determining the tracheobronchial airway pressure bycontinuous or intermittent detection and analysis of the intra-cuffpressure prevailing in the cuff of the tube inserted into the trachea.The flow of breathing gas in the ventilator is controlled as a functionof the detected intra-cuff pressure.

Advantageous embodiments of the method of this invention are discussedin this specification and in the claims. A system for assisted orcontrolled ventilation of a patient with a ventilator having a breathinggas source and a ventilator tube according to this invention has a tubethat can be introduced into the trachea and has a cuff of amicrothin-walled elastic plastic film with a wall thickness of ≦0.02 mmand can be subjected to a fill pressure ≦25 mbar. There is a measuringinstrument (electronic pressure transducer) for detecting the intra-cuffpressure prevailing in the cuff of the tube, and the values for theintra-cuff pressure, ascertained continuously or intermittently by thepressure transducer unit, can be delivered to the control algorithms ofthe ventilator via a measuring line.

Also according to this invention, the use of a tracheal tube ortracheostomy tube with an inflatable cuff of a microthin-walled elasticplastic film with a wall thickness ≦0.02 mm, which cuff has a supplyline for compressed air for setting a fill pressure of a maximum of 25mbar and has a measuring instrument for continuous or intermittentdetection of the intra-cuff pressure prevailing in the cuff, forcontrolling the breathing gas flow of a ventilator using the detectedintra-cuff pressure in the tube introduced into the trachea of apatient.

The use according to this invention of a gastric probe, having anesophageally placed balloon of a microthin-walled elastic plastic filmwith a wall thickness of ≦0.02 mm is achieved. The gastric probe has asupply line for compressed air for setting a fill pressure in theballoon of approximately 25 mbar and a measuring instrument (electronicpressure transducer) for the continuous or intermittent detection of theesophageal pressure prevailing in the balloon, in order to control thebreathing gas flow of a ventilator on the basis of the detectedesophageal pressure of the balloon.

According to this invention, there is a method and a system for assistedor controlled ventilation by a ventilator and its control using trachealtubes and tracheostomy tubes, which have microthin-walled cuffs orgastric probes that are equipped with a microthin-walled balloon. Withthe microthin-walled cuff or the esophageal balloon, thetracheobronchial airway pressure fluctuations, or the fluctuations inthe intrathoracic pressure are detected and used to improve theinteraction of the patient and the ventilator (respirator).

Tracheal tubes with a microthin-walled cuff are known from German PatentDisclosure DE 198 45 415 A1, and gastric probes that have an esophagealballoon are known from German Patent Disclosure DE 197 24 096 A1.

According to this invention, the tubes and gastric probes are used todetect the tracheobronchial airway pressure or thoracic pressure andhave a measuring instrument for detecting the intra-cuff pressureprevailing in the cuff, or the esophageal pressure prevailing in theesophageal balloon, respectively.

The cuff or balloon for the tracheal tube/tracheostomy cannula, or theballoon for the gastric probe, is preferably made from a stretchablethin plastic film with a wall thickness of less than 0.02 mm, and inparticular a wall thickness in the range from 0.01 to 0.005 mm. The cuffor balloon can be subjected, according to this invention, with a fillpressure of ≦25 mbar, and preferably to a fill pressure in the rangebetween 10 and 20 mbar. The plastic film may comprise a thermoplasticpolyurethane elastomer, and it should have a tension modulus of at least10 MPa at 300% expansion in accordance with ASTM D 412.

According to this invention, particular mechanical properties of suchmicrothin balloon films define one important field of use forcontrolling ventilators. The microthin-walled cuff or balloon of aventilator tube or gastric probe makes it possible to detect pressurefluctuations inside the tracheobronchial airway, or inside the chest(intrathoracic pressure) with high measurement precision and over a wideamplitude range, largely without latency. The measurement option of suchextremely thin-walled balloon films is possible due to their lowoperating pressures (fill pressures). Even at fill pressure values of 10mbar, highly efficient sealing off from secretions, for example, or fromthe respiration pressure exerted on the balloon can be achieved withsuch balloons, even if the exerted pressure briefly exceeds the fillpressure of the balloon. Also, the membrane-like nature of such filmsmakes it possible to detect even the tiniest pressure fluctuationsinside the balloon, or structures communicating transmurally with theballoon, and submit them to a measurement.

The tracheobronchial or intrathoracic pressure is thus detectablecontinuously, in the form of a multiply usable parameter, forcontrolling the respiration of a ventilator or for monitoring therespiratory mechanics of a patient by detecting the intra-cuff pressurethat prevails inside the cuff of the tube located in the trachea, ordetecting the balloon pressure prevailing in a balloon placed inside theesophagus of the patient.

The detection according to this invention of the tracheobronchialpressure via the intra-cuff pressure or intrathoracic pressure via theesophageal balloon pressure opens up new options for a ventilator andfor controlling the breathing gas flow.

According to this invention, by detecting the actually prevailing airwaypressure in the tracheobronchial region, it is possible to control theventilator-controlled ventilation gas flow to avoid overpressuresituations inside the deep airways.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is described below along with further features, andincluding the details shown in the drawings, wherein:

FIG. 1 is a graphical representation showing the course of thetracheobronchial airway pressure during a breathing stroke;

FIG. 2 is a graphical representation showing typical ventilationsituations in conventional pressure-triggered and pressure-assistedventilation;

FIG. 3 is a graphical representation showing the ventilation situationin esophageally triggered and pressure-assisted ventilation;

FIG. 4 is a graphical representation showing the various pressurecourses of a breathing stroke for the sake of direct measurement of ΔP(pressure drop along the tube from flow-dependent flow resistance in thetube lumen);

FIG. 5 schematically shows a tracheal tube with a cuff in longitudinalsection;

FIG. 6 is a block diagram showing assisted and controlled ventilation bya ventilator;

FIGS. 7 and 8 are work graphs illustrating various ventilationsituations; and

FIG. 9 shows a gastric probe with a balloon according to one embodimentof this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 6 shows a function diagram for assisted or controlled ventilationof a patient P, into whose trachea a tracheal tube 1, shown in FIG. 5,is introduced, in order to introduce the breathing gas AG and detect theairway pressure by suitable measuring instruments. On the one hand, theintra-cuff pressure Pcuff is detected continuously and delivered to acontrol device ST for the ventilator BG. The control device includes ameasured value and signal processor with an evaluation unit, and inaccordance with the detected intra-cuff pressure Pcuff, it furnishes asignal S for controlling the ventilator. This signal is used, forexample to control either the trigger (tripping a ventilation stroke) inassisted ventilation, or the pressure limiting function (maximal or“upper ventilation pressure”), for example, which is included in allmodes of ventilation. Accordingly, with this signal S, the supply ofbreathing gas AG from the ventilator BG to the patient P is controlled.It is also possible to equip the ventilator with a pressure regulator DRfor the fill pressure FD of the cuff of the tracheal tube 1 as well,with which regulator the supply of compressed air DL for filling thecuff in accordance with the desired cuff pressure, such as 15 mbar inthe neutral state (end of the exhalation phase of the patient), can beregulated. The pressure regulator can also be designed for periodic orintervallic readjustment of the desired cuff pressure, for instance atintervals of 60 seconds. A measuring instrument for detecting theventilation pressure Pprox at the proximal end of the tube 1 is alsoprovided, which furnishes a measured value to the control device ST.Furthermore, the control device can have a monitor M, on which workgraphs are shown to illustrate the various ventilation situations, suchas shown in FIGS. 7 and 8.

The measurement of the tracheobronchial airway pressure, which prevailsat the distal end of the tube introduced into the trachea of a patient,is possible by using a tracheal tube 1, shown as an example in FIG. 5,with a microthin-walled cuff 14; the cuff fill pressure FD can bereduced to the very low range, from 10 to 25 mbar.

FIG. 5 shows the tracheal tube 1, with a lumen 13 that is continuousfrom the proximal end 10 to the distal end 11. A standardized tubeconnector 10, for instance for a Y-piece of the ventilation tubing, isprovided on the proximal end. On this end, the ventilation pressurePprox is detected by a measuring instrument, not shown, used toascertain the flow resistance of the tube 1. Near the distal end 11, athrough hole 17 is embodied in the wall 12 of the tube 1. On the outsidenear the distal end 11 of the tube 1, but before the through hole 17,the inflatable cuff 14, of a microthin plastic film comprising athermoplastic elastomer, with a wall thickness of 0.005 mm, for example,is secured tightly to the tracheal tube 1 in the region 14 a, 14 b. Asupply line for compressed air DL, with the aid of which the cuff 14 isinflated at a fill pressure FD, leads into the interior of the cuff. Forsupplying the compressed air to the cuff, a conduit 18 is, for example,machined into the wall of the tube 1 and emerges from the wall 12 of thetube 1 in the region of the cuff 14, through the opening 19. The conduit18 leads in the direction of the proximal end 10 of the tube 1, and asupply line 15 for the compressed air is introduced into the conduit 18at the point 15 a. The proximal end of the supply line 15 has amonitoring balloon 16 and a connection 16 a, through which thecompressed air DL for inflating the cuff 14 is supplied when the desiredfill pressure FD, such as 10 mbar, is reached. At the distal end of thetube 1, the tracheobronchial airway pressure Ptrach prevails. In thecuff 14, the intra-cuff pressure (Pcuff) prevails, which in the neutralstate is equivalent to the fill pressure. If the tracheobronchial airwaypressure Ptrach is higher than the intra-cuff pressure Pcuff of the cuff14, which is equivalent to the fill pressure, then the highertracheobronchial pressure Ptrach is transmitted to the cuff and raisesthe intra-cuff pressure until there is a pressure equilibrium, or inother words Pcuff is equal to Ptrach. This process that plays out duringthe ventilation is shown in FIG. 1. In FIG. 1, the tracheobronchialairway pressure and the intra-cuff pressure are plotted in mbar over onebreathing stroke; the course over time t is plotted on the horizontalaxis. The cuff fill pressure FD is 10 mbar, for example. During theneutral phase, without the delivery of breathing gas (end-expiratoryphase), in the time periods ta, the intra-cuff pressure Pcuff equals thefill pressure of 10 mbar. During the breathing stroke, identified by theincrease in the tracheobronchial airway pressure Presp up to the maximumairway pressure Ppeak, the intra-cuff pressure Pcuff increasesanalogously, practically without delay, because the tracheobronchialairway pressure is transmitted to the cuff without latency. During theperiod tx, the intra-cuff pressure Pcuff accordingly corresponds to theprevailing tracheobronchial airway pressure Presp (Ptrach).

The intra-cuff pressure (Pcuff) passively follows the airway pressurePresp. Because the tracheobronchial airway pressure Presp is transmittedin the region of the distal end of the tube introduced into the tracheato the cuff, or the intra-cuff pressure prevailing inside the cuff,without delay, the tracheobronchial airway pressure can be measuredcontinuously in the range B in which Presp is greater than Pcuff, bydetecting Pcuff. If the tracheobronchial airway pressure Presp exceedsthe fill pressure FD in the cuff, then the intra-cuff pressure Pcufffollows the airway pressure exerted tracheobronchially on the cuff andpresses the cuff with its microthin envelope against the tracheal wallwith minimum delay. Because of the immediate, inertia-free deformationof the microthin-walled cuff, self-sealing is assured, which seals offfrom the exerted gas pressure reliably even in ventilation at aventilation pressure that markedly exceeds the fill pressure of thecuff.

For recording the intra-cuff pressure, the ventilator can be expandedwith a module with a pressure regulator which is integrated with thecontrol device and sets the desired pressure in the cuff, automaticallyreadjusts it, and continuously makes the intra-cuff pressure available,for instance in the form of a digitized signal, for controlling theventilator.

On the basis of the continuous or intermittent measurement of theintra-cuff pressure with tracheal tube/tracheostomy cannulas with amicrothin-walled cuff, the following functions can be performed forpatients ventilated by machine: the tracheobronchial airway pressurePtrach can be measured or calculated at the distal end of the trachealtube; the upper ventilation pressure limit (Pmax) of the ventilator canbe oriented to the measured intra-cuff pressure Pcuff, and thus to thetracheobronchial airway pressure Ptrach at the distal end of thetracheal tube; the ventilation, in pressure-supported orpressure-controlled ventilation methods, can be oriented to the measuredintra-cuff pressure Pcuff and thus to the tracheobronchial airwaypressure Ptrach at the distal end of the tracheal tube, as a targetventilation pressure to be reached; the pressure difference ΔP to begenerated by the ventilator in order to overcome the flow resistance ofthe tracheal tube can be ascertained simply, by measuring the intra-cuffpressure Pcuff in accordance with the tracheobronchial airway pressurePtrach, by subtracting it from the proximal airway pressure, and fromone breathing stroke to another can thus be adapted to the particularcurrent flow resistance of the tracheal tube; and on the basis ofintrathoracic fluctuations caused by the mechanics of breathing, in theintra-cuff pressure Pcuff, the triggering of the ventilator can beaccomplished synchronously with the instant of onset of the thoracicrespiratory motion of the patient.

In a further embodiment of this invention, for optimizing the control ofthe ventilator, a gastric probe, such as the gastric probe 20 shown inFIG. 9, for introduction into the esophagus of the patient can beprovided, equipped with an inflatable balloon 22 that can be subjectedto a fill pressure ≦25 mbar through a fill lumen 24, and the esophagealballoon pressure prevailing in the balloon of the gastric probe can beascertained continuously or intermittently. The gastric probe 20 candesirably be used in combination with any tube, such as described above,for insertion into a patient's trachea and having an inflatable cuff.The fluctuations in the intrathoracic pressure that are transmitted tothe balloon of the gastric probe are detected and evaluated and suppliedto the ventilator for controlling the breathing gas flow. By inflationof its esophageal balloon, the gastric probe that can be introduced intothe esophagus is placed against the wall of the esophagus, which in itsmiddle third and lower third transmits the pressure course inside thethorax through the wall of the esophagus (transmurally) to theesophageally placed balloon of the gastric probe. The transmurallytransmitted pressure is picked up by this balloon and made usable as ameasured value and control signal.

Because of the continuous characterization of the intra-esophageal(intrathoracic) pressure course by the balloon of a gastric probe, whichcan also be a nutrition probe, with an esophageally placed balloonfilled with a low pressure, it is possible: to optimize thesynchronization of the ventilator and the patient, and for example toachieve latency-free triggering of the ventilator and the best possiblecalibration over time of the ventilation cycles or respiratory cycles ofthe ventilator and the patient, respectively; and to characterize theindependent respiratory performance of the patient continuously overtime and to gain parameters in the form of feedback for the therapist.

The ventilation planning ventilation should be oriented as closely aspossible to the current respiratory capacity of the patient.

The proportion of the patient's independent respiratory performance thatis not machine-supported should be neutralized, or reduced to thegreatest possible minimum, by machine compensation, oriented to thecourse of the esophageal balloon pressure, of breathing strokes that arevolumetrically ineffective or only minimally volumetrically effective,by supportive but volumetrically ineffective breathing strokes.

By the combined use, according to this invention, of such control of thecourse of ventilation, oriented to the intra-esophageal balloonpressure, with monitoring of the respiratory work performed by thepatient during ventilation, which according to this invention isparticularly easy for the therapist and is intuitively accessible, onegoal is to enable the earliest possible weaning of ventilated patientsfrom the ventilator in a way that is oriented strictly to the success ofventilation, and particularly an increase in the patient's respiratorywork.

In the method of this invention, the esophageal balloon pressure in theballoon of the gastric probe introduced into the esophagus is measuredby a measuring instrument, and the measured values are transmitted by ameasuring line that extends from the balloon to the ventilator or to acontrol device for the ventilator. The values obtained by measuring theesophageal balloon pressure are used to characterize the respiratorywork done by the patient, and from pressure-supported respiratory cyclesof fixed duration, cyclical respiratory work graphs are ascertained anddisplayed on a monitor in the form of pressure-volume loops.

The intra-cuff pressure of the tube is also measured by a measuringinstrument, and the measured values are transmitted by a measuring lineextending from the cuff of the tube to the ventilator, or to a controldevice for the ventilator. In order to detect the esophageal pressure,equivalent to an intrathoracic pressure, the system for assisted orcontrolled ventilation of a patient using a ventilator with an airsource has a gastric probe with an inflatable balloon of amicrothin-walled elastic plastic film with a wall thickness of ≦0.02 mm,and the gastric probe balloon is subjected to a fill pressure of ≦25mbar. A measuring instrument for detecting the esophageal balloonpressure prevailing in the gastric probe balloon is also provided, andthe values for the esophageal balloon pressure, detected continuously orintermittently by the measuring instrument, can be delivered to thecontrol device of the ventilator via a measuring line. To set a desiredfill pressure in the gastric probe balloon, a measuring and regulatingdevice is provided, which is integrated with the control device of theventilator. For setting a desired fill pressure in the cuff of the tubeintroduced into the trachea of a patient, it is also possible to providea measuring and regulating device for the fill pressure, which isintegrated with the control device of the ventilator.

By measuring the tracheobronchial airway pressure via the intra-cuffpressure in the cuff of the tube introduced into the trachea, it ispossible according to this invention, for the pressure difference ΔP tobe generated by the ventilator in order to overcome the flow-dependentflow resistance of the tube, to be ascertained in accordance with thepressure difference between pressure Pprox at the proximal end of thetube and the tracheobronchial airway pressure Ptrach at the distal endof the tube, by measuring the pressure at the proximal end of the tubeand by measuring the intra-cuff pressure, and to be adapted to theapplicable flow resistance of the tube from one breathing stroke toanother during the ventilation with the ventilator.

It is also proposed that a certain differential value of the intra-cuffpressure be predetermined as a trigger threshold for the ventilator, andthat it trip the supporting machine ventilation stroke if the intra-cuffpressure drops at the onset of inspiration, which is synchronous withthe intrathoracic pressure drop. The values, obtained by measuring theintra-cuff pressure, can be used to control the “upper pressurelimitation” (Pmax) function of the ventilator, so that on reaching apredetermined allowable upper airway pressure in the trachea that mustnot be exceeded, the ventilator either switches off the supply ofbreathing gas or switches over to exhalation.

The individual method steps and equipment options according to thisinvention are further explained below.

Orientation of the ventilator with respect to the pressure limitation ofthe upper ventilation pressure Pmax to the intra-cuff pressure Pcuff canbe considered.

If the tracheobronchial airway pressure (Ptrach) exceeds an upperventilation pressure value Pmax that is to be input at the ventilator,then the machine ventilation stroke ceases, or the valves of theventilator switch to expiration for immediate relief. Conventionalventilators measure the airway pressure Presp at the proximal or outerend of the tracheal tube, or in the tubing of the ventilator. The airwaypressure Ptrach that actually prevails in the lungs can not beascertained directly by conventional equipment technology at the distalend of the tracheal tube. Known ventilators are thus equipped with anoption for compensating for the flow-dependent tube resistance(automatic tube compensation), in the form of a computerizedapproximation of the airway pressure (Ptrach), prevailing at the distalend of the tube, by a compensating algorithm, which is oriented to thesize of the tracheal tube used (inside diameter), which must be inputmanually in the ventilator when ventilation begins, and as a consequenceis only oriented to the flows measured in the equipment.

The option of actually measuring the tracheobronchial airway pressure atthe distal end of the tube by means of the tube cuff, in its function asa sensor element, offers the intra-cuff pressure as a reliablemeasurement variable for the function of an upper ventilation pressurelimit (Pmax), or for the discontinuance of the machine breathing stroke,at critically high pressures.

Above all in ventilation using pediatric tubes with a very small insidediameter, in conventional ventilation partial shifting of the tube caneasily occur, for example from secretions or kinking of the tube. Thetracheobronchial airway pressure in conventional ventilation can thusdeviate considerably from the proximal airway pressure measured beforethe tube. According to this invention, the tracheobronchial airwaypressure, ascertained at the distal end of the tube via the intra-cuffpressure, and the measured proximal airway pressure of the tube areascertained and compared by the control device of the ventilator. If ano longer plausible difference is exceeded, for instance if the pressuremeasured proximally before the tube is considerably higher than theairway pressure (intra-cuff pressure) or Ptrach measured at the distalend is implausibly higher than the pressure measured before the tube,then an alarm can be tripped.

A further option for the ventilator is to orient the desired ventilationpressure, in pressure-controlled or pressure-supported respiration, tothe intra-cuff pressure. Ideally, the ventilation pressure to which thebreathing gas supply to the patient is subjected should be oriented tothe tracheobronchial airway pressure, not to a ventilation pressure(which as a rule deviates from it) of the kind that prevails forinstance at the proximal end of the tube and is typically measuredthere. Particularly for ventilating children, this is decisive, becausein children the airway pressure established tracheobronchially must notbecome overly high. Because tracheal tubes for children have a verysmall inside diameter, a backup pressure can easily build up between thedistal end of the tube and the associated ventilation tracts, because ofthe high flow resistance of small tubes, a greater volume can enter thelungs upon active machine ventilation (inhalation) than can escape fromthe lungs upon the passive exhalation.

Orientation of the ventilator with respect to pressure support orpressure-controlled ventilation to the intra-cuff pressure can beconsidered.

In ventilation situations in which the ventilation pressure in thetrachea (Ptrach) exceeds the intra-cuff pressure Pcuff, the respiratorypressure built up by the ventilator, for instance in pressure-supportedventilation or controlled modes of ventilation, can be oriented to theintra-cuff pressure of the cuff of a tracheal tube introduced into thetrachea of the patient, which pressure is a controlling measuredvariable. By measuring the effective tracheobronchial airway pressurevia the intra-cuff pressure, as shown by FIG. 1, the user gains agenuine parameter measured in the patient's lungs, and thus gainsadditional certainty and precision in ventilation with a ventilator,such as shown in FIG. 6.

If Ptrach is less than Pcuff, or if the cuff pressure can no longerreflect the course of the ventilation pressure, then the ventilatororients itself in the conventional way to the proximal airway pressurePprox measured before the tube. In pressure-supported orpressure-controlled modes of ventilation, the entire course of theventilation pressure can be oriented to the central course of theventilation pressure.

With the pressure support by the ventilator, a tracheobronchial pressureis built up and controlled, and the desired pressure is maintained.

For optimizing the compensation for the flow-dependent resistance of thetracheal tube, the pressure difference between the tracheobronchialairway pressure at the tip of the tube (Ptrach) and the ventilationpressure (Pprox) measured at the proximal end of the tracheal tube isdetermined from one breathing stroke to another.

The conventional ventilation equipment option of so-called automatictube compensation calculates a corresponding pressure difference to beimposed by the ventilator. The pressure difference is equivalent to thepressure required to overcome the flow-dependent flow resistance of thetube. It is oriented to a corrective constant that uses the insidediameter of the tracheal tube as a basis for calculation. The insidediameter of the tube is input manually at the onset of ventilation andis thus fixed over the further course of ventilation.

The automatic tube compensation is done by conventional technology inaccordance with the following algorithm, for example, ΔP=const×flow², inwhich ΔP represents the compensatory pressure to be calculated.

Changes in the inside diameter of the tracheal tube, for example frompartial kinking, or shifting/stopping up of the tracheal tube withsecretion which creates resistance during ventilation, are notrecognized by the compensatory algorithm in conventional ventilators andcan be recognized by the user only in the form of an increase in theproximal ventilation pressure Pprox measured before the tube. Thecompensatory algorithm cannot, however, follow transitory changes in theinside diameter of the tube and thus in the flow resistance, and theresult is compensation that is largely inappropriate to the actualsituation.

According to this invention, ΔP to compensate for the flow-dependenttube resistance can be ascertained by measuring the airway pressure inthe trachea (Ptrach) via the intra-cuff pressure, in those regions ofthe ventilation pressure curve where Ptrach exceeds the fill pressure ofthe cuff, Pcuff, or in other words in the range tx.

In this pressure range, ΔP can therefore be measured directly andwithout any relative chronological latency, using the equationΔP=Pprox−Pcuff, and is therefore superior to the above-describedcompensatory approximation based on a rigid, nondynamic constant.

In the ventilation pressure range above the cuff fill pressure, forexample of 15 mbar at the cuff, the corrective constant const can becalculated continuously from the measured pressure difference ΔP, bysolving the equation for the constant const (const=flow²:ΔP).

The corrective constant thus ascertained can then be used for currentlyadapted compensation of the complete next breathing stroke (using theequation ΔP=const×flow²).

Tracheal tubes and tracheostomy cannulas that have microthin-walledcuffs furthermore, in a patient who is spontaneously breathing, alsomake it possible to detect fluctuations in the intrathoracic pressurecaused by the mechanics of breathing. The effect is especiallypronounced whenever the cuff is placed in the thoracic segment of thetrachea, as is almost always the case in patients with tracheostomies.

Particularly in small children and the newborn, intrathoracic pressurechanges are transmitted virtually simultaneously and with relativelygreat amplitude via the tracheal wall (transmurally) to the cuff andthus affect its fill pressure.

The special sensing qualities of microthin balloon membranes forembodying the cuff of tracheal tubes and tracheostomy cannulas (or theballoons of gastric probes) make extremely sensitive, latency-freedetection of such fluctuations in the intrathoracic pressure possibleand open up additional options for controlling a ventilator.

Optimizing the synchronization of the ventilator and the patient can beconsidered.

To trip a supported machine breathing stroke, the patient, by breathing,must generate or trigger a predetermined inspiratory minimum flow, orminimum pressure drop in the tubing of the ventilator. In order togenerate such a trigger signal, however, the patient must overcome notonly the resistances of the thorax and the lungs and as anend-expiratory pressure (intrinsic PEEP) that can burden the alreadydiseased lungs, but also the resistances of the ventilator tube and thedelivery tubing.

In FIG. 2, a typical ventilation situation in conventionalpressure-triggered, pressure-assisted ventilation is shown. The courseover time is plotted on the horizontal axis T, and the pressure P isplotted in millibars on the vertical axis.

The upper curve ID shows the intra-esophageal (intrathoracic) pressurecourse.

The lower curve shows the airway pressure Presp.

The time a represents the onset of thoracic inspirational motion, theonset of inhalation.

The instant b marks the end of the thoracic inspirational motion, theonset of exhalation.

At c, a discrete attempt at inspiration by the patient causes a slightdrop in the ventilation pressure in the tubing that supplies thepatient. If this pressure drop exceeds a certain value (triggerthreshold), the supporting breathing stroke is tripped. This istime-offset from the actual onset a of inspiration. The respiratory workperformed by the patient in the interval between a and c can in manycases lead to respiratory fatigue of the patient. Frustrating attemptsby the patient to breathe, during which because of the inadequatetrigger sensitivity of conventional ventilators no supporting stroke canbe tripped, only hasten respiratory fatigue.

Particularly in patients with existing pulmonary disease, such asobstructive pulmonary disease, the respiratory work that has to be doneto trigger the ventilator can be considerable and can lead to physicalrespiratory fatigue in the patient. The assisted ventilation hastherefore until now, in many cases, had to be repeatedly disrupted andthen continued with intermittent alternation with a controlled,completely machine-specified mode of ventilation.

Moreover, particularly in patients with existing pulmonary disease, alarge proportion of the respiratory efforts fail to be detected by theventilator, even if the trigger thresholds are set quite sensitively,see FIG. 2. The thoracic breathing work is considerable but does notsuffice to generate an equipment-triggering pulse (minimum gasflow/minimum pressure drop). The respiratory effort by the patient istherefore not supported by the ventilator.

According to this invention, it is possible to design the ventilationsuch that the interaction between the patient and the ventilator isoptimized, and respiratory fatigue in assisted modes of ventilation isavoided, absolutely to the greatest extent possible.

If at the onset of inspiration the thoracic volume is increased (raisingof the chest, lowering of the diaphragm), if a proportional drop in theintrathoracic pressure occurs, if the cuff of the tracheal tube ortracheostomy cannula is placed in the thoracic portion of the trachea,then the intrathoracic pressure is also transmitted through the trachealwall to the cuff pressure.

If the pressure at the onset of inspiration drops by a predetermined,freely selectable value (trigger threshold), then the machine-supportedbreathing stroke is tripped. This shortens the length of time between aand c in FIG. 2. Because there is only a slight delay between the onsetof the thoracic breathing effort and the onset of machine support, thetriggering work to be performed in order to trip the supporting strokescan be reduced to a minimum. Trigger-dictated respiratory fatigue in thepatient, as is observed above all in the phase of respiratoryinsufficiency at the instant of transition from long-term controlledventilation to assisted ventilation, can thus be avoided.

The instant of triggering, ascertained both in the cuff and in thetubing of the ventilator, can be compared in the ventilator, or itscontrol device, and if a no longer plausible difference, such as thetrigger time cuff pressure, is exceeded, for instance if the triggeringinstance cuff pressure occurs later than the triggering instant in thetubing, or in the event of complete asynchronism, this leads to an alarmor a discontinuance of the cuff-triggered ventilation, and a switchoverto a conventional trigger mode.

To further shorten the chronological latency between the onset ofthoracic respiratory effort and the onset of machine support, thisinvention proposes the alternative triggering on the basis of anautocorrelative recognition of a curve segment typical for the onset ofinspiration (the initial drop in the intra-cuff pressure curve at theonset of thoracic breathing). This pattern curve segment is comparedwith the ongoing intra-cuff pressure signal by an autocorrelationalgorithm.

The correlation coefficients (from 0 to +1) ascertained serve as atrigger criterion. The user specifies a minimum correlation to beattained as the trigger threshold (for instance, +0.88). If this valueis reached, the supporting machine stroke begins. The pattern curvesegment to be correlated can be averaged at regular intervals(arithmetic averaging) or on a continuous sliding basis (for instance, arunning average) from a selectable number of previous inspiratory curvesegments.

This invention combines triggering on the basis of thoracic pressurefluctuations (via the cuff of the tracheal tube or tracheostomy cannula,or via the esophageal balloon of a suitably equipped gastric probe) withan intermittent mandatory pressure-supported ventilation.

In the ventilation mode of this invention, the number ofmachine-assisted breathing strokes per minute is specified by the user(mandatory ventilation). Based on the number of mandatory ventilationstrokes, the minute is divided into intervals of equal duration (timeslots). Within these time slots, only a single machine-assistedbreathing stroke at a time can be tripped by the patient. All the otherrespiratory efforts or respiratory excursions of the patient within thistime slot are unsupported by the ventilator. The respiratory work isthen predominantly done by the patient within the context of thesebreaths that are not machine-supported.

Triggering the ventilator on the basis of intrathoracic pressurefluctuations caused by respiratory mechanics can also be done using agastric probe with an esophageal balloon, as described in German PatentReference DE 197 24 096 A, which is used for long-term, functionallyorganically tolerated balloon secretion sealing (no transporting of theballoon toward the stomach, no relevant pressure maximums inside theballoon during peristaltic contractions).

With such a balloon placed esophageally, changes in the intrathoracicpressure course can also be monitored, and the measured esophagealballoon pressure can be made useful, in the same way as the intra-cuffpressure, for controlling the assisted ventilation.

Machine compensation for respiratory efforts that are not, or are onlyslightly, flow-effective or volumetrically effective, are discussedbelow.

To enable the early transition to an assisted ventilation pattern uponeven the least independent breathing by the patient, a ventilator shouldhave the option of maximally relieving the respiratory mechanics of thepatient as needed.

This invention thus proposes compensating for spontaneous, nonsupportedrespiratory efforts with insufficient or low volumetric performance(insufficient tidal volume without affecting gas exchange) by an adaptedmachine ventilation stroke, in such a way that in conjunction with thepressure measurement values obtained from the esophageal balloon of thegastric probe, the esophageal balloon pressure curve in the course ofthe thoracic inspiratory motion is returned to the range of the basal,neutral balloon fill pressure of the gastric probe. The respiratory workdone in the context of nonsupported respiratory efforts can thus belargely neutralized by machine compensation, referring to FIG. 3.

In FIG. 3, the minimized triggering work in esophageally triggeredpressure-assisted ventilation is shown. Here the respiratoryneutralization of unproductive, unsupported inspiratory efforts isshown. The upper course represents the intra-esophageal (intrathoracic)pressure course ID.

The lower curve shows the airway pressure Presp attained by the assistedventilation.

In the range a, the triggering ensues as a result of a drop inesophageal pressure upon the onset of thoracic inspiratory motion; thechronological latency until the onset of machine ventilation istherefore minimally small (minimal triggering work by the patient).

At b, a breathing stroke that neutralizes the patient's breathingmechanism is shown, which after esophageal triggering, by suitablyadapted course of ventilation pressure, returns the esophageal pressurecurve to the baseline (position of repose). The thoracic breathing workperformed by the patient during an inspiratory effort is thus reduced tothe greatest possible minimum, and the tidal volume also is in the rangeof idle volume ventilation; no gas exchange, or no relevant gasexchange, takes place. The intrathoracic pressure course ID isascertained by measuring the esophageal balloon pressure of the gastricprobe inserted into the esophagus. The compensatory success of aventilation stroke adapted in this way is oriented and fed back to theintra-esophageal pressure course.

The compensation could, for instance if combined with intermittentmandatory pressure-supported ventilation, be designed so that it becomesactive after the conclusion of a mandatory stroke and remains activeuntil the end of a given time slot.

With synchronized intermittent mandatory pressure-assisted ventilationand compensation or neutralization activated in this way, the patient'srespiratory work then occurs solely in the context of the machinepressure-supported mandatory strokes. By adapting the machine support(for instance varying the initial inspiratory flow and/or theinspiratory ventilation pressure) in a way oriented to the patient'srespiratory work graph (tidal volume over esophageal balloon pressure),the proportion of independent respiratory work to these mandatorystrokes can likewise be reduced to a minimum.

Thus the training of the patient's respiratory work can be adapted,based on a state of maximum possible respiratory relief, incrementallyto the gradually increasing respiratory performance of the patient.

For example, such ventilation planning could begin with an intermittentreduction in the support by the mandatory strokes (reduction in theinitial flow and/or inspiratory pressure). If sufficient breathing bythe patient persists (which can be detected from the increased thoracicdeflection in the work graph and from the virtually constant tidalvolume), the machine support in the form of the mandatory strokes can beincreasingly restricted. In addition, the machine compensation for(neutralization of) spontaneous nonsupported breathing strokes can bereduced incrementally or terminated. In a final phase, by reducing thenumber of supported mandatory breathing strokes, the trainingperformance of the patient can then be increased by the correspondinglyincreased number of unsupported breathing strokes, until finally themandatory strokes can be dispensed with entirely.

Monitoring the patient's respiratory work is discussed below.

Respirators and ventilators of conventional design are not equipped tomonitor the patient's respiratory work on the basis of genuinerespiratory function parameters measured in the patient. Although therespirator does ascertain such variables as tidal volume, ventilationpressure and the breathing flow, a characterization to be achievedintuitively by the user of the current or medium-term and long-termeffect of a selected ventilation regime on the respirator efficiency ofthe patient, however, has until now been unavailable.

In conventional monitoring, the respiratory fatigue of the patientcannot be prevented in advance by correcting the machine ventilationparameters, as a rule. The success or failure of a ventilation regimehas thus until now been predominantly interpreted from the clinicalaspect (onset of respiratory fatigue with tachypnea) or changes in theblood gases (respiratory acidosis).

As an essential component of this invention, a continuouscharacterization of respiratory work curves (esophageally via the tidalvolume) in a special form is proposed, as a quasi-optimized interfacewith the user, and these curves can then be shown for instance on amonitor M in a ventilator as shown in FIG. 6.

One goal of the respiratory monitoring according to this invention isthe earliest possible transition from a controlled to an assisted formof ventilation, or faster weaning from the respirator in a way orientedstrictly to the mechanical respiratory performance of the patient.

It is preferable according to this invention for spontaneouslymachine-supported and unsupported breathing strokes to be plotted on thesame coordinate system as the work graph.

The work graphs of individual pressure-supported breathing strokes showwhether the current choice of parameters (initial inspiratory volumetricflow, inspiratory pressure to be attained, PEEP) lead to the desiredscope of respiratory relief of the breathing strokes of the patient.

The respiratory work graphs of non-machine-supported breathing strokes,conversely, make an approximate assessment of the successive respiratorytraining possible (decreasing respiratory work (respiratory fatigue),stagnant or increased respiratory work (further reduction in machinesupport)).

To integrate the course over time (trend) in the respiratory work withthe monitor unit (cyclical respiratory work graphs) for the sake ofventilation planning, this invention proposes the following modes ofcharacterization.

The applicable current respiratory work cycles are shown in the form ofan uncorrected original signal, for instance in the color red. In orderto characterize the effective training for the particular equipmentsetting in an easily interpreted way via a medium-term to long-termperiod on the monitor, the respiratory cycles (loops) are statisticallyaveraged every 5 minutes, for instance, and the resultant loop is thenshown on the monitor in the form of a representative respiratory workcurve for the applicable period of time. The loop is assigned aparticular color value, such as light blue.

The procedure is then continued in the same way with the respiratorycycles in ensuing time intervals. The loop then calculated is assignedthe same color value as the preceding curve (light blue). The colorvalue of the preceding loop, conversely, then shifts successively to adarker blue value. The respiratory history of the patient can thus beintegrated into the monitor unit in a way that is easy for the user tointerpret, from the shift in the color values, for instance from lightblue to dark blue.

The ventilation parameters used during a time segment can be madevisible, for instance by activating the appropriate loop in a window onthe screen.

Optionally, the color change from light to dark, in the cycles averagedevery 5 minutes, for instance, can be done exclusively in the event ofchanges in the ventilation parameters.

To display and check the synchronization of the patient and therespirator, it is optionally possible to incorporate the ventilationpressure and/or ventilation flow (measured in the machine system) andthe intrathoracic pressure (measured in the esophageal balloon) into thedisplay, in the form of a curve over time.

It is also conceivable for the absolute value of the respiratory workperformed in supported and unsupported strokes to be displayed (in eachcase as a separate curve) in joules over time.

Spontaneous stationary, non-peristaltic, so-called secondarycontractions of the esophagus are expressed, in the intrathoracicpressure curve, by brief, steeply rising pressure increases.

Such curve courses can be detected as such from predeterminedautocorrelation patterns and recorded in terms of their frequency. Theydo not enter into the statistical averaging of the loops and are eithernot shown, or shown only optionally, in the display on the monitor.

In a corresponding way, peristaltic or so-called primary contractions ofthe esophagus are detected and handled as gradually rising and fallingintra-esophageal pressure increases that last several seconds.

The monitoring according to this invention can also be used, inconventionally triggered, pressure-supported modes of ventilation, inso-called BIPAP ventilation, or in proportionally assisted ventilation(PPSV), for a choice of ventilation parameters that is oriented closelyto the current respiratory capacity of the patient.

In conventional assisted ventilation patterns, it is known that thepatient inhalation is in many cases not yet concluded while therespirator is already in the exhalation mode. The converse case ofmachine-assisted ventilation beyond the end of the inhalation efforts bythe patient is also often observed. The autocorrelative signal analysisof the intra-esophageal pressure curve for instance also makes itpossible to terminate the assisted ventilation stroke synchronously withthe conclusion of the thoracic inspiratory motion on the part of thepatient.

Analogously to the onset of ventilation, the duration of the assistedstroke can be adapted to the patient's breathing (correlation of thecontinuous intra-esophageal pressure signal with a pattern signal thatis morphologically typical for the end of inspiration).

Two work graphs according to this invention, schematically shown inFIGS. 7 and 8, and possible ventilation situations are described asexamples. In FIG. 7, a spontaneous, intermittent mandatorypressure-supported ventilation is shown which is typically calledpressure support ventilation, or PSV.

In the work graph of FIG. 7, the tidal volume is plotted in ML on thevertical coordinate, over the esophageal balloon pressure Pesoph inmmHg, plotted horizontally, is plotted as a work graph for therespiratory work of the patient. The respiratory cycles are shown as aloop, specifically by statistical averaging over 5 minutes. The currentloop in each case is shown unaveraged and in red as an original signalover a respiratory window (60 sec./number of mandatory strokes).

The averaged loops, each representing an interval of a specified numberof minutes, such as 5 minutes, are designated by a through d and pertainin FIG. 7 to unassisted spontaneous breathing.

The loops marked A through D in FIG. 7 relate to mandatory machinepressure-supported spontaneous breaths. Individually, the loops are asfollows:

(a) pronounced thoracic respiratory excursions with low tidal volume(idle volume breathing) corresponding to dark blue;

(A) high inspiratory pressure with resultant high tidal volume,extensive respiratory relief of the patient's respiratory musculaturereduction in the assisted component (pressure support);

(b) compensation for the low respiratory minute volume by supportedrespiratory work in the unassisted spontaneous breaths (increased tidalvolume);

(B) tidal volume drops; partial compensation for the supported componentby forced respiratory work by the patient (increased thoracicrespiratory work) positive training effect at constant machineparameters;

(c) increase in the non-supported respiratory work by the patient withincreasing tidal volume;

(C) increasing contribution by the patient to the breathing stroke withan increase in the tidal volume further reduction in the pressuresupport;

(d) progressive success in training, increasing tidal volume withconstant thoracic respiratory work corresponding to light blue; and

(D) the reduction in the pressure support is compensated for while thetidal volume stays constant.

One goal is gradual approximation of the unsupported and the supportedrespiratory work curves.

In FIG. 8, the work graph is shown for a flow-compensated andvolume-compensated patient ventilation in the proportional pressuresupport or PPS mode. Once again, the tidal volume here is plotted overthe esophageal balloon pressure. The loops a through e shown are eachrepresentative of an interval of predetermined minutes, such as 5minutes, and relate to proportional flow-compensated andvolume-compensated assisted ventilation. Individually, the loops showthe following:

(a) The patient is too weak to generate a volumetric flow which meansthat for such patients, PPS is unsuitable. A change to an esophageallytriggered pressure-supported ventilation, such as the PSV mode, isnecessary; and

(b) The loops b through e show that the patient does generate anadequate volumetric flow; continuous increase in the respiratory work isbrought about by incremental empirical adaptation of the options offlow-compensation and volumetric-compensation of the PPS mode to thepulmonary elasticity and resistance.

A monitor M, which shows the work graphs of FIGS. 7 and 8, can forexample, be assigned to the control device of the ventilator of FIG. 6.Accordingly, the requisite patient parameters should then be measuredand supplied to the control device.

1. In a method for controlling a flow of breathing gas in a ventilatorfor assisted or controlled ventilation of a patient as a function of atracheobronchial airway pressure of the patient, having one of aventilator tube, a tracheal tube and a tracheostomy tube, which can beintroduced into a trachea of the patient and can be subjected to thebreathing gas and which has an inflatable cuff and at least one lumenthat is continuous from a distal end of the ventilator tube to aproximal end of the ventilator tube, and wherein an airway pressure isdetected, the improvement comprising: determining the tracheobronchialairway pressure by one of continuous and intermittent detection andevaluation of an intra-cuff pressure prevailing in the cuff of the tubeinserted into the trachea, and controlling the flow of the breathing gasin the ventilator as a function of a detected intra-cuff pressure,determining a pressure difference (ΔP) generated by the ventilator toovercome a flow resistance of the tube as a function of the pressuredifference between the pressure at the proximal end of the tube and thetracheobronchial airway pressure at the distal end of the tube bymeasurement of the pressure at the proximal end of the tube and theintra-cuff pressure, and using a ΔP to calculate a compensatoryconstant, and adapting dynamically the compensatory constant from onebreathing stroke to another breathing stroke during respiration by theventilator, to a respective current flow resistance of the tube.
 2. Inthe method of claim 1 wherein the cuff is subjected to a fill pressure≦25 mbar.
 3. In the method of claim 2, wherein the cuff is subjected toa fill pressure ≦15 mbar.
 4. In the method of claim 3, wherein the tubewith the cuff of a stretchable thin plastic film with a wall thicknessof less than 0.02 mm is used.
 5. In the method of claim 4, wherein thecuff is made from a film of thermoplastic polyurethane elastomer with amodulus of tension of at least 10 MPa at 300% expansion in accordancewith ASTM D 412, and is used for the tube.
 6. In the method of claim 5,wherein a differential value that trips a breathing stroke of theventilator is specified in a cuff fill pressure as a trigger thresholdfor the ventilator, and if an intra-cuff pressure drops during an onsetof thoracic inspiration by the patient to below the trigger thresholdthe ventilator is activated and trips a machine-supported breathingstroke.
 7. In the method of claim 6, wherein during controlledrespiration, values obtained by measuring the intra-cuff pressure areused to control an upper pressure function of the upper pressure limit(Pmax) of the ventilator so that the ventilator on attaining apredetermined upper pressure one of switches off a delivery of thebreathing gas and switches over to exhalation.
 8. In the method of claim7, wherein for optimizing control of the ventilator, a gastric probehaving an inflatable balloon that can be subjected to a fill pressure of≦25 mbar is introduced into an esophagus of the patient, and anesophageal balloon pressure prevailing in the balloon of the gastricprobe is detected one of continuously and intermittently, and pressurefluctuations in an intrathoracic pressure transmitted to the gastricprobe balloon are detected and evaluated and supplied to the ventilatorfor controlling the flow of breathing gas.
 9. In the method of claim 8,wherein the intra-cuff pressure of the tube is measured by a measuringinstrument, and measured values are transmitted by a measuring line thatextends from the cuff of the tube to one of the ventilator and a controldevice for the ventilator.
 10. In the method of claim 9, wherein theesophageal balloon pressure in the balloon of the gastric probeintroduced into the esophagus is measured and second measured values aretransmitted from the balloon to one of the ventilator and a controldevice for the ventilator.
 11. In the method of claim 10, wherein valuesobtained by measuring the esophageal balloon pressure are used toascertain a respiratory work done by the patient, and from breathingstrokes pressure-supported by the ventilator of respiratory cycles offixed duration cyclical breathing work diagrams are determined anddisplayed on a monitor as one of loops and areas.
 12. In the method ofclaim 1, wherein the cuff is subjected to a fill pressure ≦15 mbar. 13.In the method of claim 1, wherein the tube with the cuff of astretchable thin plastic film with a wall thickness of less than 0.02 mmis used.
 14. In the method of claim 1, wherein the cuff is made from afilm of thermoplastic polyurethane elastomer with a modulus of tensionof at least 10 MPa at 300% expansion in accordance with ASTM D 412, andis used for the tube.
 15. In the method of claim 1, wherein adifferential value that trips a breathing stroke of the ventilator isspecified in a cuff fill pressure as a trigger threshold for theventilator, and if an intra-cuff pressure drops during an onset ofthoracic inspiration by the patient to below the trigger threshold theventilator is activated and trips a machine-supported breathing stroke.16. In the method of claim 1, wherein for optimizing control of theventilator, a gastric probe having an inflatable balloon that can besubjected to a fill pressure of ≦25 mbar is introduced into an esophagusof the patient, and an esophageal balloon pressure prevailing in theballoon of the gastric probe is detected one of continuously andintermittently, and pressure fluctuations in an intrathoracic pressuretransmitted to the gastric probe balloon are detected and evaluated andsupplied to the ventilator for controlling the flow of breathing gas.17. In the method of claim 1, wherein the intra-cuff pressure of thetube is measured by a measuring instrument, and measured values aretransmitted by a measuring line that extends from the cuff of the tubeto one of the ventilator and a control device for the ventilator.
 18. Ina method for controlling a flow of breathing gas in a ventilator forassisted or controlled ventilation of a patient as a function of atracheobronchial airway pressure of the patient, having one of aventilator tube, a tracheal tube and a tracheostomy tube, which can beintroduced into a trachea of the patient and can be subjected to thebreathing gas and which has an inflatable cuff and at least one lumenthat is continuous from a distal end of the ventilator tube to aproximal end of the ventilator tube, and wherein an airway pressure isdetected, the improvement comprising: determining the tracheobronchialairway pressure by one of continuous and intermittent detection andevaluation of an intra-cuff pressure prevailing in the cuff of the tubeinserted into the trachea, and controlling the flow of the breathing gasin the ventilator as a function of a detected intra-cuff pressure, andduring controlled respiration, using values obtained by measuring theintra-cuff pressure to control an upper pressure function of the upperpressure limit (Pmax) of the ventilator so that the ventilator onattaining a predetermined upper pressure one of switches off a deliveryof the breathing gas and switches over to exhalation.
 19. In the methodof claim 18, wherein a pressure difference (ΔP) generated by theventilator to overcome a flow resistance of the tube is determined as afunction of the pressure difference between the pressure at the proximalend of the tube and the tracheobronchial airway pressure at the distalend of the tube by measurement of the pressure at the proximal end ofthe tube and the intra-cuff pressure, and a ΔP is used to calculate acompensatory constant, and the compensatory constant is adapteddynamically from one breathing stroke to another breathing stroke duringrespiration by the ventilator, to a respective current flow resistanceof the tube.
 20. In a method for controlling a flow of breathing gas ina ventilator for assisted or controlled ventilation of a patient as afunction of a tracheobronchial airway pressure of the patient, havingone of a ventilator tube, a tracheal tube and a tracheostomy tube, whichcan be introduced into a trachea of the patient and can be subjected tothe breathing gas and which has an inflatable cuff and at least onelumen that is continuous from a distal end of the ventilator tube to aproximal end of the ventilator tube, and wherein an airway pressure isdetected, the improvement comprising: determining the tracheobronchialairway pressure by one of continuous and intermittent detection andevaluation of an intra-cuff pressure prevailing in the cuff of the tubeinserted into the trachea, and controlling the flow of the breathing gasin the ventilator as a function of a detected intra-cuff pressure,measuring an esophageal balloon pressure in the balloon of the gastricprobe introduced into the esophagus and transmitting second measuredvalues from the balloon to one of the ventilator and a control devicefor the ventilator, and measuring values obtained by the esophagealballoon pressure and using the values to ascertain a respiratory workdone by the patient, and from breathing strokes pressure-supported bythe ventilator of respiratory cycles of fixed duration determiningcyclical breathing work diagrams and displaying them on a monitor as oneof loops and areas.